This application pertains to the art of pressurized fluid conduction. More particularly, the invention relates to connecting above ground and below ground conduits through which pressurized fluids are conducted. The invention is particularly applicable to risers for connecting below ground natural gas service lines above ground with meters and other fluid receiving members. It will be appreciated, however, that the invention has other applications including channelling other subterranean utilities such as water, electric power or telephone lines, fuel oil, and the like above ground.
Historically, natural gas has been conveyed in heavy iron and steel pipes. These heavy pipes were relatively short, on the order of 8 to 20 feet, and required frequent connections. More recently lighter weight and more corrosion resistant conduits have been replacing the iron pipe. Continuous length tubing, i.e., tubing that is sold in reels of 50 feet, 100 feet, or longer, greatly reduce the amount of labor for installation. For service lines, plastic tubing in continuous lengths from reels is perhaps the most common, although conduits of copper, aluminum, plastic and metallic composites, and the like are also common. The plastic and other conduits, particularly tubing which is sufficiently flexible to be sold on reels, lack the impact, fracture, cutting and abrasion resistance of iron and steel pipe. They tend to fail prematurely at elevated temperatures and tend to become brittle at low temperatures. This increases the danger of the conduit losing its gas conducting integrity when impacted by a lawnmower, gardening tool, snow shovel, or the like. Accordingly, many building codes require an impact resistant riser, frequently specifying iron or steel, where a natural gas conduit leaves the ground and enters the meter or building.
The change in conduit construction as it emerges from the ground necessitates a gas impermeable seal between the conduit and impact resistant riser. Most commonly a gas impermeable connection is between plastic and steel. The gas impermeable connection must maintain its integrity under temperature extremes, under impacts, under stresses exerted by different coefficients of expansion, rough handling by installers, and the like. To assure the integrity of the connection, elaborate or redundant multiple seals are commonly used. The forming of multiple connections and seals increases the cost of risers without, necessarily, improving their reliability. Examples of multiple seal interconnections between plastic or other conduit and a steel riser are shown in U.S. Pat. No. 4,085,950, issued Apr. 25, 1978 to Sam Alewitz.
The present invention contemplates a new and improved riser apparatus and method of manufacture which overcomes all of the above-referenced problems and others. It provides a riser which is simple and economical to manufacture, yet securely connects plastic or other conduits with a steel or other high strength riser.